Britain could be better off if it "quits" the European Union than if it remains a member, Boris Johnson has said.

The London Mayor made his comments ahead of the publication of a new report, which finds London's economy would not suffer significantly if the UK headed for the exit.

Mr Johnson, who will make a speech on the report on Wednesday, is expected to set out an eight-point plan for reform of the EU, which will far exceed the renegotiation deal being attempted by the Prime Minister.

"When you look at the cost of EU social policy, the stagnation of the EU economies, the continuing absurdities of some Brussels regulation, we are plainly getting to the stage where it might well be better to quit an unreformed EU than to stay in," Mr Johnson wrote in his column for The Daily Telegraph.

Mr Johnson will go further than the PM on renegotiation terms

"As it happens, I have no doubt that we can lead the campaign for reform. But if we are going to succeed, we need to build on our alliances, and to appreciate how our friends on the continent see things."

It comes amid increasing speculation over whether the London mayor will stand for MP in 2015 and a possible subsequent bid for the Tory leadership should David Cameron fail to deliver at the ballot box next year.

The comments could also pit Mr Johnson against Chancellor George Osborne, also a potential leadership contender, who will be giving a speech on Tuesday.

And it will put pressure on Mr Cameron to be clear about whether he will campaign to leave the EU if he fails to gain a better deal for the UK come a promised in-out referendum in 2017.

The report, which has been drawn up by Mr Johnson's senior economic adviser Gerard Lyons, will say a British exit from the European Union is "definitely a viable option".

It is expected to find the capital's GDP of £350bn, which accounts for about a fifth of the UK economy, can be expected to grow to £640bn by 2034 if Britain stays in a reformed EU. However, it finds if Britain exits the EU, London's GDP would still grow to £614bn by 2034.

It comes as Nick Clegg calls for a limit on the number of migrants arriving from new EU countries.

He wants EU countries to be able to close the door if there are too many people from the new member states trying to come in.